1. Field of the Invention
This invention relates to novel catalysts for the polymerization of olefins. This invention especially relates to the use of an intermediate drying step for the production of improved catalysts. These improved catalysts are to be employed with cocatalyst for use in the polymerization of olefins to polyolefins such as polyethylene, polypropylene and the like, or copolymers such as ethylene copolymers with other alpha-olefins and diolefins. The intermediate drying step imparts unusually high activity and improved hydrogen response to the catalyst and the polymer product obtained has a desirable bulk density. The improved catalysts are especially useful for the production of linear polyethylenes such as high density and linear low density polyethylene. The polymer product obtained evidences an important balance of polymer properties, for example, the catalyst system obtains a polymer with a narrow molecular weight distribution and an improved balance in polymer product machine direction tear strength and transverse direction tear strength. As a result, the film blown from resin produced from the catalyst manifests an overall high strength.
The improved catalyst comprises a solid reaction product obtained by contacting a solid, particulate, porous support material such as, for example, silica, alumina, magnesia or mixtures thereof, for example, silica-alumina, with an organometallic composition treated with an alcohol, drying to a free flowing solid then contacting the solid in stages with an acyl halide, a transition metal compound, a halogen containing compound, halogen or interhalogen and prereducing the solid in the presence of an organoaluminum compound. The intermediate drying step provides an improved catalyst component, which when used with an aluminum alkyl cocatalyst, produces the improved catalyst system of this invention which can be usefully employed for the polymerization of olefins.
The catalyst system can be employed in slurry, single-phase melt, solution or gas-phase polymerization processes and is particularly effective for the gas phase production of linear polyethylenes such as high density polyethylene and linear low density polyethylene.
2. Description of the Prior Art
Recently, interest has arisen in the use of magnesiumtitanium complex catalyst components for the polymerization of olefins. For example, European patent application No. 27733, published Apr. 29, 1981 discloses a catalyst component obtained by reducing a transition metal compound with an excess of organomagnesium compound in the presence of a support such as silica and thereafter deactivating the excess organomagnesium compound with certain deactivators including hydrogen chloride.
U.S. Pat. No. 4,136,058 discloses a catalyst component comprising an organomagnesium compound and a transition metal halide compound, which catalyst component is thereafter deactivated with a deactivating agent such as hydrogen chloride. This patent does not teach the use of support material such as silica, but otherwise the disclosure is similar to the above-discussed European patent applica- tion.
U.S. Pat. No. 4,250,288 discloses a catalyst which is the reaction product of a transition metal compound, an organomagnesium component, and an active non-metallic halide such as HCl and organic halides containing a labile halogen. The catalyst reaction product also contains some aluminum alkyls.
Catalyst components comprising the reaction product of an aluminum alkyl-magnesium alkyl complex plus titanium halide are disclosed in U.S. Pat. Nos. 4,004,071 and 4,276,191.
U.S. Pat. Nos. 4,173,547 and 4,263,171, respectively disclose a catalyst component comprising silica, an aluminum-type titanium trichloride and dibutyl magnesium and a catalyst component comprising a magnesium alkyl-aluminum alkyl complex plus titanium halide on a silica support.
The use of chlorine gas in polymerization processes is taught in U.S. Pat. No. 4,267,292 wherein it is disclosed that chlorine gas is to be added to the polymerization reactor after polymerization has been initiated in the presence of a Ziegler catalyst. U.S. Pat. No. 4.248,735 teaches subjecting a silica support to a treatment with bromine or iodine and thereafter incorporating a chromium compound onto the support. U.S. Pat. No. 3,513,150 discloses the treatment of gamma alumina plus titanium tetrachloride with a gaseous chlorinating agent and employing said treated material in combination with a cocatalyst for the polymerization of ethylene.
European patent application 32,308 discloses polymerizing ethylene in the presence of a catalyst system comprising an organic metal compound and a titanium-containing material which is obtained by reacting together an inert particulate material, an organic magnesium compound, a titanium compound and a halogen containing compound such as SiCl.sub.4, PCl.sub.3, BCl.sub.3, Cl.sub.2 and the like.
Each of U.S. Pat. Nos. 4,402,861, 4,378,304, 4,388,220, 4,301,029 and 4,385,161 disclose supported catalyst systems comprising an oxide support such as silica, an organomagnesium compound, a transition metal compound and one or more catalyst component modifiers. These patents do not disclose the catalyst of this invention.
In British No. 2,101,610 silica is treated with a magnesium alkyl, an alcohol, benzoyl chloride and TiCl.sub.4. In each of Japanese Kokai Nos. 56-098206 and 57-070107 acyl halides are employed during the preparation of titanium supported catalysts.
The catalyst systems comprising magnesium alkyls and titanium compounds, although generally useful for the polymerization of olefins such as ethylene and other 1-olefins, do not show excellent responsiveness to hydrogen during the polymerization reaction for the control of molecular weight, do not readily incorporate comonomers such as butene-1 for the production of ethylene copolymers, do not show an extremely high catalytic activity and obtain polymer product whose film properties are unbalanced under anisotropic conditions.
In U.S. Pat. No. 4,451,574 issued May 29, 1984, a catalyst system obtained by treating an inert particulate support, such as silica, with an organometallic compound, a titanium halide and a halogen gas is disclosed. Although the catalyst obtains very high activities, there is a need for improving the film properties of polymer product obtained by polymerizing olefins in the presence of the catalyst and to improve the bulk density of polymer product
In Application Ser. No. 638,167 filed Aug. 6, 1984 and now U.S. Pat. No. 4,564,606 there is disclosed a transition metal supported catalyst component obtained by contacting an inert solid support with (a) the reaction product of a dialkyl magnesium compound and an alcohol, (b) an acyl halide, (c) TiCl.sub.4, and (d) Cl.sub.2. In application Ser. No. 637,641 filed Aug. 3, 1984and now U.S. Pat. No. 4,565,797 there is disclosed a transition metal supported catalyst component obtained by contacting an inert solid support with (a) the reaction product of a dialkyl magnesium compound and an oxygen-containing compound, (b) a transition metal halide such as TiCl.sub.4, (c) Cl.sub.2 and treating the resultant solid with an organometallic compound of a Group IIa, IIb or IIIa metal. Neither application discloses the use of an intermediate drying step. Although these catalysts obtain high activities and improved film properties, there is a need for improving both activity and response to hydrogen.
In accordance with this invention improved catalysts have been found which have very high catalytic activities and excellent hydrogen responsiveness for the control of molecular weight, excellent comonomer response and obtain polymer product with greatly improved film properties. The resins exhibit excellent melt strength at low extrusion power consumption, resulting in excellent bubble stability in blown film production at high extrusion rates. The invention is an improvement over pending applications Ser. No. 638,167 U.S. Pat. No. 4,564,606) and Ser. No. 637,641 (U.S. Pat. No. 4,565,797) in that the catalysts of this invention unexpectedly obtain an improvement in catalytic activity and hydrogen response providing polymers with reduced ash content and a broad range of molecular weights. These unexpected improvements are obtained by the use of an intermediate drying step during the catalyst preparation.
The new catalyst components of this invention are obtained by contacting an oxide support with an organometallic composition treated with an alcohol, drying to a free flowing solid then contacting the solid in stages with an acyl halide, a transition metal compound, a halogen or interhalogen compound, and an organometallic compound of a Group IIa, IIb or IIIa metal such as, for example, an aluminum alkyl. The catalyst system comprising the transition metal-containing catalyst component and an organoaluminum cocatalyst is advantageously employed in a gas phase ethylene polymerization process since there is a decrease in reactor fouling as generally compared with catalytic prior art ethylene gas phase polymerization processes thereby resulting in less frequent reactor shut downs for cleaning purposes.